Our virtual water network of the Roman World shows that virtual water trade and irrigation provided the Romans with resilience to interannual climate variability. Virtual water trade enabled the Romans to meet food demands from regions with a surplus. Irrigation provided stable water supplies for agriculture, particularly in large river catchments. However, virtual water trade also stimulated urbanization and population growth, which eroded Roman resilience to climate variability over time.

The paper presents results from a novel dynamical coupling between a hydrology model and a regional climate model developed to include a wider range of processes, land-surface/atmosphere interaction and finer spatio-temporal scales. The coupled performance was largely dependent on the data exchange frequency between the two model components, and longer-term precipitation was somewhat improved by the coupled system whereas the short-term dynamics for a range of variables was less accurate.